R help - Aug 2015 - Is there "orphan code" in seq.default?

I was looking at the code in seq.default and saw code that I think would throw
an error if it were ever executed, although it will not because there is first a
test to see if one of its arguments is missing. Near the end of the function
body is this code:

    else if (missing(by)) {
        if (missing(to)) 
            to <- from + length.out - 1L
        if (missing(from)) 
            from <- to - length.out + 1L
        if (length.out > 2L) 
            if (from == to) 
                rep.int(from, length.out)
            else as.vector(c(from, from + seq_len(length.out - 
                2L) * by, to))

Notice that the last call to `else` would be returning a value calculated with
'by' which was already established as missing.

-- 

David Winsemius
Alameda, CA, USA

On 08/15/2015 02:01 PM, David Winsemius wrote:
> I was looking at the code in seq.default and saw code that I think would
throw an error if it were ever executed, although it will not because there is
first a test to see if one of its arguments is missing. Near the end of the
function body is this code:
>
>      else if (missing(by)) {
>          if (missing(to))
>              to <- from + length.out - 1L
>          if (missing(from))
>              from <- to - length.out + 1L
>          if (length.out > 2L)
>              if (from == to)
>                  rep.int(from, length.out)
>              else as.vector(c(from, from + seq_len(length.out -
>                  2L) * by, to))
>
> Notice that the last call to `else` would be returning a value calculated
with 'by' which was already established as missing.
>
missing arguments can have default values

 > f = function(by="sea") if (missing(by)) by
 > f()
[1] "sea"

which is the case for seq.default

 > args(seq.default)
function (from = 1, to = 1, by = ((to - from)/(length.out - 1)),
     length.out = NULL, along.with = NULL, ...)


Martin Morgan
-- 
Computational Biology / Fred Hutchinson Cancer Research Center
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